1. Field of the Invention
The invention relates to a valve joint, in particular, valve measuring joints for fluid systems with high operating pressures. The valve joints consist of a connector bushing under line pressure and a spring loaded and mechanically actuated non-return valve arranged in the bore of the connector bushing.
2. Background of the Prior Art
Valve joints of the above-mentioned type serve, for example, to establish testing or measuring connections to pressure lines where, as a rule, the connector bushing having external threads is installed fixedly in the pressure line of, for example, hydraulic or pneumatic systems. For the duration of the testing or measuring operations, a seal nipple in the form of a hollow pin is screwed onto the connector bushing by means of a union nut joined fixedly with a hose. These joints may be connected, for example, under pressure, i.e. without deactivating the installation, through measuring lines with the corresponding measuring instruments. In the case of permanently installed instruments (for example, manometers, selective manometer switches and pressure switches) the flexible measuring lines may be installed in the manner of electric cables, so that expensive pipe installations may be avoided. Effective working pressures may be measured directly on the hydraulic device by means of such measuring connections without the need for the release of vent nuts or pipe joints. Joints of this type are used in numerous structural elements and controls of hydraulic or pneumatic systems. Following the breaking of the connection, a protective cap nut is screwed onto the connector bushing having external threads to prevent the penetration of dirt into the connector bushing and to perform an additional sealing function in the event that a non-return valve installed in the bush is not absolutely tight. Valve joints of the aforementioned type are described, for example, in West German Patent No. 27 56 084, wherein the valve bodies are in the form of cones or spheres. In this known valve joint, the valve body is installed as a non-return valve on a compression spring so as to be movable by the spring. It also has a flow channel on its upper contact end. The valve joint is equipped with sealing and anti-twist gasket, the sealing function whereof is, however, assured only when a corresponding hose or cap nut is screwed tightly onto the connector bush with its seal nipple.
If the cap nut is released or if such a nut does not exist, for example in the case of selective monometer switches, the pressure medium is sealed off only by the corresponding non-return or check valve. Check valves for high pressure valve joints of this type exhibit, for reasons of design, a more or less pronounced tendency to leak depending on the viscosity of the pressure medium. In any case, these check valves cannot be produced under the conditions of assembly-line manufacturing so as to provide tight sealing in actual practice.
For hose lines in general hydraulics and for gas filling devices of hydraulic reservoirs, such configurations are adequate. But even then, there are often complaints concerning leakage if, for example, caps are released in several valve joints simultaneously in order to test several measuring locations in succession with one measuring device. Other complaints of leakage occur in the case of hydraulic reservoirs when gas pressure test devices without the possibility of refilling are used. When the valve joints are employed to monitor installations with combustible gases, leakage can also be a problem.
The use of valve joints of this type in manometer selection switches is entirely impossible because of constant leakage at the fittings not in use. Attempts have already been made in connection with the abovementioned valve joints to equip the check valve with elastic rubber seals, such as conventional O-rings. This had not led to positive results in all cases in spite of adequate initial tightness. With long measuring lines and large dead volumes in manometers (or in the circulation connected with it) and particularly with low visocsity liquids (.ltoreq.40 mm.sup.2 /sec) or in the case of higher operating pressures or in testing devices for hydraulic reservoirs, the elastic rubber gasket is washed out. This is because the high difference in pressure upon the lifting of the valve causes a very strong flow of the medium used against the seal.